Filter unit



J. \I'AN LQQN FILTER UNIT Filed Sept. 22, 1934 INVENTOR ATTORNEYPatented Mar. 22, 1938 PATENT OFFICE FILTER UNIT Oarel Jan van Loon,Eindlioven, Netherlands,

notation of Delaware or to Radio Corporation of America, a cor-Application September 22, 1934, Serial No. 745,006

In Germany October 30, 1933 This invention relates generally to electricfilters and more particularly to a high ohmic resistance which is moreparticularly designed for use in a circuit arrangement for separatingdirect or alternating current from superposed high frequency alternatingcurrents.

In the accompanying drawing Figure 1 illustrates a common type of filterunit; Fig. 2 illus trates diagrammatically a filter unit constructed inaccordance with the present invention; Fig. 3 is a cross-sectional viewof one of the units constructed in accordance with the presentinvention, and Fig. 5 illustrates a sectional view of the device shownin Fig. 4.

Generally filters consist of a number of series resistances and parallelcondensers as shown in Fig. 1. The filter sections are constituted hereby resistances n, r: and condensers C1, C2. The arrangement shown in thedrawing may serve, for instance, as a coupling between the outputcircuit of a detector tube and the input circuit of an amplifying tubein a radio receiving set, in which it is of particular importance thatthe high frequency oscillations do not reach the lowirequency amplifierpart.

The present invention provides a resistance construction in which theresistances and con densers form an assembly.

According to the invention a high resistance consisting of an insulatingsupport and of a thin resistance layer applied thereon, is entirely orpartly coated with a conductive layer that is separated from theresistance layer by a thin insulating layer. The resistance layer is tobe considered as a condenser plate, whereas the other plate isconstituted by the conductive layer which preferably consists of metalsquirted thereon. As a dielectric an extremely thin lacquer layer may beused. The assembly may be arranged in the manner shown in Fig. 2, inwhich R denotes "the resistance and C the conductive layer.Consequently, the resistance according to the invention constitutes afilter having a uniformly divided resistance and capacity. This has theadvantage that the condensers may be dispensed with. It has been foundthat the resistance according to the invention affords an excellentfilter working.

The invention is particularly adapted for use with a cylindrical highohmic resistance.

In Figure 3 the preferably tubular resistance support is denoted by I.As a material for this support porcelain or another suitable insulatingmaterial may be used, 2 being the resistance support that may beprovided by means of a suitable known method. Numerals 3 and 3' are themetal junction caps engaging the resistance layer and being connected tothe connecting wires 4 and I. The resistance layer is coated with aninsulating layer 5 on to which the good conducting layer 6 5 is appliedto which a conductor is connected. It has turned out that the capacityavailable between the layers 2 and 6 is completely sufilcient forrealizing the filter working necessary for high frequency currents.

An excellent filter working may be ensured by providing the resistancelayer and the conductive layer in such a manner that there are severalsurfaces which are separated from each other and at which the resistancelayer and the conl5 ductive layer cover each other. In this manner anumber of condensers is produced in which the corresponding plates aremutually connected by resistance or conductive material. This may berealized inter alia by squirting the resistance only 20 locally withmetal at a number of points and by interconnecting the conductivesurfaces by separate conductors.

A very simple form of construction of such a resistance is obtained whenusing a resistance 25 element having a helical resistance layeraccording to Figure 4. The metal coating may be provided as a stripparallel with the axis of the cylinder. Now the assembly is no longer afilter having a uniform capacity'and resistance, but it 3''} constitutesa filter circuit with a large number of cells that may have such a sizethat the best filter working is ensured. It goes without saying that theconductive layer need not be provided according to a generatrix, butthat it may also ex- 5 tend helically, for instance, along thecircumference of the cylinder.

I claim:

1. An electric filter connected in the line between 9. source of energyand a utilizing circuit 40 comprising an insulating support havingapplied to it a thin layer of high ohmic resistance material around oneof the surfaces thereof, said layer of resistance material forming aresistance element, a layer of insulating material applied to 5 theouter surface of the layer of resistance material, a condenser element,said layer of resistance material forming one plate of the condenserelement, the other plate of the condenser element comprising a thinlayer of conducting material 50 formed around at least a portion of theouter surface of the layer of insulating material, said resistanceelement being connected in series with the line and said capacitiveelement being connected in shunt with the line.

0 formed around at least a portion oi the outersuriaceoitbelayerotinsulatingmateriaLan input terminal, an outputterminal and a common terminal, means for connecting one end of saidribbon of resistance material to the input terminal, means forconneetinzthe output terminal to the other end of the ribbon oiresistance material, and means for connectins the common terminal to thelast named plate of the condenser.

cam JAN was LOON. 1

